noun
Particle Physics an uncharged nucleon having a mass of c. 1.675×10 kg (c. 939.5729 MeV/c, c. 1,839 times the mass of an electron): a free neutron, as in nuclear fission, has a half-life of c. 14.8 minutes, is readily absorbed by a nucleus, and decays into a proton, an electron, and a neutrino